1. Field of the Invention
The present invention generally relates to methods for removing lead from lead-contaminated wastes and particularly from used lead storage batteries and battery debris piles. More specifically, the present invention is directed to a plurality of environmentally favorable methods useful to control dust and environmental contamination and to recover the removed lead, together with clean scrap/recyclable ebonite, hard rubbers and plastics. The methods of the present invention employ both hydromechanical separation processes and chemical separation processes using more environmentally acceptable chemicals than those employed in the prior art.
2. Description of the Background
Lead acid storage batteries are comprised of a plurality of lead plates immersed in a sulfuric acid electrolyte solution contained within a non-conductive case, typically comprised of plastic or hard rubber, e.g., ebonite. Plates of opposite polarity are insulated from one another by means of porous separators. Electrochemical power is drawn from the plates through conductive lead alloys forming terminals and joined to the plates. The chemically active materials are sponge lead at the cathode and lead dioxide at the anode. When these active materials are electrically connected in the presence of sulfuric acid, an oxidation-reduction reaction creates electrochemical energy and converts the lead materials to insoluble lead sulfate. Water, produced as a by-product of the reaction, reduces the concentration of sulfuric acid. As the lead is converted to lead sulfate and the concentration of electrolyte reduced, the battery output weakens and the used battery is scrapped.
As a result of the oxidation-reduction from which electricity is produced, used or scrapped batteries, in addition to containing lead and lead dioxide, also contain significant quantities of lead sulfate in a weak sulfuric acid solution. Scrap batteries have generally been considered valuable only for their lead content. Accordingly, many patents are directed to methods for recovering the lead from scrap batteries. For example, see U.S. Pat. Nos. 4,118,219, 3,689,253, 3,393,876 and 3,300,043 which disclose various smelting and chemical methods for recovering lead from scrap batteries.
Separate and apart from lead recovery are the environmental problems resulting from used or scrapped batteries, scrap lead and other materials contaminated by lead. As environmental knowledge and standards have increased, the need to process scrap batteries and other lead-contaminated materials has increased. These environmental problems have increasingly become important in connection with the clean-up of manufacturing, storage and scrap sites contaminated by lead. The clean-up and removal of lead contamination from such sites and the materials stored there without producing secondary contamination through windblown, lead-contaminated dust or discharge of water contaminated with lead or other chemicals has taken on a new importance.
Of particular concern is the desire to extract the contaminating lead in a recoverable form while producing scrap material having an acceptable lead content and, particularly, an acceptable extractable or leachable lead content which might permit the recovered materials to be recycled. Accordingly, a need has developed for methods for extracting lead contaminants from the plastic and ebonite portions of used storage batteries. Methods to produce scrap materials, e.g., ebonite and plastics, meeting more stringent leachable lead concentrations, whether merely for scrap or for recycle, have intensified.
The methods of the present invention which provide the ability to recover recyclable materials during the clean-up operations and thus to minimize disposal and storage offer significant advantages over the prior art. The present invention provides methods capable of reducing the leachable lead content of scrap ebonite and plastic below 5 ppm when determined by the Extraction Procedure Toxicity test (EPTox). The EPTox test procedure is set forth at EPA Method 1310. The present invention offers methods for meeting even more rigorous standards, e.g., leachable lead determined by the Toxicity Characteristic Leaching Procedure (TCLP), which may be applied in the future. The TCLP test procedure (EPA Method 1311) is set forth at 40 C.F.R. Part 261, Appendix II.
Accordingly, the present invention has provided methods for meeting the long felt but unfulfilled need for environmentally safe methods of processing lead-contaminated materials and reducing the lead and leachable lead content of various materials, e.g., scrap plastics, ebonite, other hard rubbers and other lead-contaminated materials, to provide clean scrap or recyclable materials.